Much effort has been expended to provide a hinge to extruded plastic. This is because there are important commercial benefits in providing such a hinge. First, if a sheet of extruded plastic can be bent or folded, this makes the plastic sheet much easier to handle, store and transport. This is especially the case where the sheet of plastic is large. And second, a sheet of extruded plastic that can be bent or folded has commercial applications, such as a box or a container.
For example, U.S. Pat. No. 4,921,563 ("the '563 patent") discloses a method for making foldable plastic products. The '563 patent discloses an extruding apparatus having three rollers defining two nips, where the first nip is used to form a sheet of plastic material having a predetermined thickness and the second nip is used to cool the sheet of plastic material. Only after the sheet of plastic material has cooled and solidified, is a stationary cutting tool employed to provide an L-shaped slit in the sheet which serves as a hinge for the plastic sheet.
There are disadvantages associated with the extruding apparatus of the '563 patent. First, because the sheet of plastic material must be properly cooled and solidified prior to the cutting procedure, there is an associated delay in the manufacturing process. And second, it has been found that cutting a cooled and solidified plastic sheet may tend to cause cracks or fractures in the plastic where such a cut is made. Introduction of cracks or fractures in a sheet of plastic is undesirable because of the significant detrimental effect on the integrity of the plastic sheet.
U.S. Pat. No. 5,169,651 ("the '651 patent") discloses a scoring apparatus for forming a fold line for boxboard window material, such as PVC film. The '651 patent does not disclose an extruder. The scoring apparatus has a series of heated creasing rollers which, as a film of plastic is drawn through the apparatus, provide a groove of successively increasing depth to the plastic film. Downstream of the creasing rollers is a heated caliper roller which flattens shoulders surrounding the groove formed by the creasing rollers. The caliper roller also penetrates the groove to a depth less than that of the last creasing roller to finally form the groove in the plastic film.
There are disadvantages associated with the scoring apparatus of the '651 patent. First, since the apparatus does not disclose an extruder, the film must be reheated before it can be scored. Second, although the heated creasing rollers and the heated caliper roller may be adjusted vertically to alter the depth of a groove, there is no means provided to modify the location of a groove with respect to the plastic film. Thus, with the scoring apparatus of the '651 patent, there is no expeditious way to provide fold lines at different locations on successive batches of plastic sheets. And third, the scoring apparatus of the '651 patent does not provide expeditious adjustment of the size and shape of a groove to be formed on the plastic film. In order to modify the size and shape of the groove, all of the heated creasing rollers and the heated caliper roller must be replaced, which would entail significant costs and time delay.
Another prior art method for providing a hinge to a sheet of plastic is disclosed in U.S. Pat. No. 3,320,225 ("the '225 patent"). The '225 patent discloses an extrusion apparatus having two pressure rolls defining a nip. At least one of the rolls has formed integrally thereon a ridge for providing a groove to a sheet of plastic.
The apparatus of the '225 patent has disadvantages similar to those associated with the scoring apparatus of the '651 patent. First, there is no means provided to modify the location of the groove with respect to the sheet of plastic. Thus, there is no expeditious way to provide hinges at different locations on successive batches of plastic sheets. And second, the apparatus of the '225 patent does not provide expeditious adjustment of the size and shape of a groove to be formed on the sheet of plastic. In order to modify the size and shape of the groove, it is required that the pressure roll or rolls with the ridge formed integrally thereon be replaced, thereby entailing significant costs and time delay.
Prior attempts to provide a hinge to extruded plastic have been problematic for the disadvantages discussed above. What is desired, therefore, is a method and apparatus for providing a hinge to extruded plastic, while it is still warm and wherein the location, size and shape of the hinge can be readily modified in an expeditious and economical manner.